Gretna officials issued a boil-water advisory for the city Thursday after a routine inspection by the state found E. coli and other coliform bacteria in the water supply.

The state collected the samples Wednesday and got the positive test results Thursday morning. It notified the city about 9:30 a.m., and Mayor Belinda Constant’s office issued the advisory about 11:30 a.m.

The state is conducting another round of tests, which should produce results by about noon Friday. If those tests show there was a flaw in the initial test or that the samples were contaminated during collection, the advisory could be lifted.

In the meantime, Gretna residents are asked to boil water for three minutes before drinking it or using it to bathe, make ice, wash food, shave or brush their teeth.

Residents in the 70053 ZIP code are affected; the advisory does not include Timberlane Estates and unincorporated areas of West Jefferson surrounding the city that are often referred to as Gretna. Those areas get their water from Jefferson Parish’s government.

“We’re investigating every possibility at this point in time,” Constant said, noting the system has been flushed and the chlorine levels verified.

She also said Jefferson Parish agreed to test samples in tandem with the testing being done by the state to provide an extra layer of certainty.

Coliform bacteria, which include E. coli, can make people sick and are a particular concern for infants, young children and people with weakened immune systems. They can turn up in the water supply if it has been contaminated by human or animal waste.

Symptoms include diarrhea, cramps, nausea and headaches.

The city hasn’t issued a boil-water advisory since 2001, and that one stemmed from a loss of pressure at the plant, not a positive sample, City Attorney Mark Morgan said.

Constant said the city has spent $11 million upgrading its water system — $25 million if work on the sewer system is included — over the past 10 years.

She said Gretna’s water is tested by the state every day, though the test that found the E. coli is one that is conducted monthly.

New Orleans’ Sewerage & Water Board issued a boil-water advisory late last month after power failed at its main pump station. The agency took seven hours to make the announcement, drawing criticism from City Council members. There ultimately was no problem with the water.

Follow Chad Calder on Twitter, @Chad_Calder.